Investigation of cohesive FE modeling to predict crack depth during deep-scratching on optical glasses

Optical glass scratching can induce various types of cracks, among which median cracks are extremely detrimental and penetrate deeply under the surface. Due to deep-scratching process complexity, it is challenging to devise a method to predict median crack depth. Indentation testing has been examined comprehensively in prior research works. It has been found that using the correlation between scratch and indentation testing can simplify predictive method development. In this research, a numerical method based on indentation testing is proposed to determine median crack depth during deep scratching. In the first step, an FE model is configured to simulate the indentation testing process and the Cohesive Zone Method is applied to describe median crack behavior. The cohesive parameters calibrated through experimental indentation testing are implemented in the FE scratch model, and the results are compared with the experimental scratch test results. According to the results, the FE scratch model was enhanced by mode II fracture energy and the modeled friction coefficient. The indentation and scratch experiments were conducted with BK7, F2, Fused silica, K5, Pyrex, Quartz, SF6, and SF19. The experimental results prove that the nonlinearity of the median crack depth curve correlates with K_Ic. A comparison of the experimental and numerical results demonstrates the model is virtually functional for materials with K_Ic below 1000?kPa?m^1/2. Comparisons between the current findings and other studies infer the model and experimental results are accurate and reliable.     

Performance of Holstein and Swedish-Red × Jersey/Holstein crossbred dairy cows within low- and medium-concentrate grassland-based systems

This 2 × 2 factorial design experiment was conducted to compare the performance of spring-calving Holstein dairy cows (HOL, n = 34) with Swedish Red × Jersey/Holstein crossbred (SR × J/HOL, n = 34) dairy cows within low and medium concentrate input grassland-based dairy systems. The experiment commenced when cows calved and encompassed 1 full lactation. Cows were offered diets containing grass silage and concentrates [70:30 dry matter (DM) ratio, and 40:60 DM ratio, for low and medium, respectively] until turnout, grazed grass plus either 1.0 or 4.0 kg of concentrate/d during the grazing period (low and medium, respectively), and grass silage and concentrates (85:15 DM ratio, and 70:30 DM ratio, for low and medium, respectively) from rehousing and until drying off. No significant genotype × system interactions were present for any of the feed intake or full-lactation milk production data examined. Full-lactation concentrate DM intakes were 769 and 1,902 kg/cow for the low and medium systems, respectively, whereas HOL cows had a higher total DM intake than SR × J/HOL cows in early lactation, but not in late lactation. Although HOL cows had a higher lactation milk yield than SR × J/HOL cows, the latter produced milk with a higher fat and protein content, and thus fat plus protein yield was unaffected by genotype. Milk produced by the SR × J/HOL cows had a higher degree of saturation of fatty acids than milk produced by the HOL cows, and the somatic cell score of milk produced by the former was also higher. Throughout the lactation, HOL cows were on average 30 kg heavier than SR × J/HOL cows, whereas the SR × J/HOL cows had a higher body condition score than the HOL cows. Holstein cows had a higher incidence of mastitis and ovarian dysfunction that SR × J/HOL cows.     

频率域电磁法在采空区探测中的应用

隐伏采空区的探测已成为近年来研究课题,采用无人机搭载发射装置,高空平面布置探测线和测点,克服在陡峭的山坡难以布置探测工作,消除地形地貌及其它条件对探测工作带的误差。对已知空区的探测和分析,验证了该方法的有效性和精确程度,为后续其它探测提供了频率域区间和参数校正。研究表明:此方法具有适用性强、工作效率高和精确度高优点,是一种可用于隐伏空区的探测方法,分析过程中可以辨别采空区变形情况。     

石墨烯增强铜基复合材料的制备技术及发展

石墨烯由于其独特的二维结构和优异的物化性能,在改善复合材料的力学性能、电学性能和热学性能等方面具有很大的潜力,已成为金属基复合材料较理想的增强体。铜合金具有优异的导电导热性能和良好的延展性,但是其强度较低、不耐磨及高温下易变形的特点阻碍了其应用和发展。因此,结合石墨烯和铜的性能特点,将石墨烯作为增强体添加到铜中,制备性能优异的石墨烯增强铜基复合材料成为目前研究的热点之一。综述了目前石墨烯增强铜基复合材料的制备方法,并对各方法的特点进行了分析比较,提出未来可采用的制备工艺的方向以及在制备过程中面临的问题和挑战,并对其未来的研究方向进行了展望。     

受阻胺类固化剂固化环氧树脂的固化过程研究

通过差示扫描量热法(DSC)研究了几种不同基团取代脂肪族二元胺中的一个氢原子所形成的三官能度脂肪胺类固化剂固化环氧树脂的过程。分别使用Kissinger模型和Flynn-Wall-Ozawa模型对三种固化剂固化环氧树脂的动力学参数进行了计算。结果表明,三种固化剂固化环氧树脂的反应活性大小比较为:N-乙基乙二胺≈N-甲基乙二胺>N-苯基乙二胺。这不仅与得到的固化度-时间曲线结果相符,并且可以从结构的角度以电子效应,共轭效应和位阻效应理论给予合理解释。N-苯基乙二胺中,由于苯环的刚性较大,空间位阻效应尤为明显,活化能(E a)在固化度(α)=0.5时为61.99 kJ/mol,而在α=0.9时达到97.63 kJ/mol,随着固化度的增加反应活性迅速下降,因此该类固化剂固化过程中更需要控制工艺。     

基于组合赋权-集对分析的煤矿煤尘爆炸危险性评价研究

针对目前煤尘爆炸危险性评价研究较少、各评价因素选择偏差较大的问题,通过分析煤尘爆炸特性,提出以煤尘可爆性危险、煤尘爆炸浓度危险、点火源危险3个必要条件为一级指标,煤质变异程度、挥发分、水分、灰分等14个二级指标,以层次分析法确定各指标的主观权重,以熵权法确定各指标的客观权重,利用乘法归一化方法对各指标的组合权重进行计算,构建集对分析-组合赋权煤尘爆炸危险性评价模型,并将该模型与已较成熟的改进FAHP模型、模糊事故树模型、灰色聚类评估体系、未确知测度评价模型一同应用于济宁某矿的煤尘爆炸危险性评价过程中,结果显示:集对分析-组合赋权评价模型、改进FAHP模型、灰色聚类评估体系评价结果为一般危险等级,模糊事故树模型的评价结果为较安全等级,集对分析-组合赋权煤尘爆炸危险性评价模型评价结果与改进FAHP模型、灰色聚类评估体系、未确知测度评价模型的评价结果一致,该模型对煤尘爆炸危险的评价具有较好的适用性。     

5429双马来酰亚胺树脂的固化动力学研究

通过差示扫描量热法(DSC)研究了5429双马树脂的固化过程。分别使用Kissinger模型和Flynn-Wall-Ozawa模型计算得到了5429双马树脂动力学参数。结果表明Kissinger模型与FWO模型计算得到的动力学参数较为接近,验证了两个动力学模型的有效性。由于5429双马树脂的固化反应为一级反应,因此代入相应的固化动力学参数可得到其固化动力学方程。此外,通过T-β外推法可计算得到5429双马树脂凝胶化温度、固化温度和后处理温度等特征温度。     

Highly durable,Pt free and large-area Ni–B film synthesized by SILAR as a bifunctional electrode for electrochemical water splitting

A search for efficient, durable, large-area, and economic catalyst material for low-cost production of hydrogen and oxygen is currently a high priority in the field of electrocatalysis (EC). In view of this, a cost-effective, earth abundant, highly stable, Pt free, and large-area (8 cm × 8 cm) bifunctional Ni–B electrocatalyst is reported via simple and economic SILAR method. A highly porous surface of Ni–B film with high surface wettability indicated better electrochemical water-splitting properties for the films and is obtained at 100 cycles. A Low over-potential value to obtain HER (49 mV) and OER (340 mV) at 10 mA/cm² current suggested that they are comparable to the well-known Pt and RuO electrodes in alkaline medium (1M KOH), respectively. In actual water-splitting setup having Ni–B film (as cathode) and stainless steel (as anode), the hydrogen production of 612 ml/h is obtained at constant potential, which was enhanced by 18% i.e., 726 ml/h when a Ni–B film as both cathode and anode electrode was used. Both the electrodes are highly stable for over 15 days and interestingly they showed 7% increment in the EC performance.     

基于离散单元法的群楼拆除爆破仿真模拟

基于青岛开发区一商场爆破工程,利用颗粒离散元法建立离散元网格实体模型,用多面体离散元法模拟分析拆除爆破中建筑物的倒塌过程。研发的网格实体模型详细模拟了建筑物从结构局部失稳到整体完全倒塌的整个过程,确定了爆堆轮廓线和爆堆尺寸,直观给出了爆破设计的效果。触地振动、冲击力变化分析结果表明:所给出的爆破方案可达到预期拆除爆破的效果,触地振动符合《爆破安全规程》要求;该模型可优化爆破设计,指导爆破施工,为建筑物拆除爆破的灾害预测与安全评估提供理论依据。